So I work for a small landscape company that's been around for about 6 years, they have about 4 crews and have gone through about 15 pieces of equipment that are no longer running. Obviously they aren't doing proper maintenance. So here's my questions from some research I've been doing.

Can a clogged spark arrester make it so you can't start it at all?
Do you need special spark plugs or a certain size for stihl equipment? And what are the effects if you have the wrong spark plug size or the gap is off?
And what's the effect of running an engine everytime until the spark plug gives out(multiple times)
How often should air filters be cleaned?

I know this is a bit of questions but I'd really appreciate it. I just started this job and I'd like to help him out.

Also if you could give me a list of things that need to be properly maintained to ensure the health of the engine I would appreciate it.

Thanks in advance for the help

Do I need sway bars when lowering my car?

I have '95 BMW 318ti and I'm looking at a Eibach pro lowering kit. But for an extra cost it includes a front and rear sway bar, do I need those? I'm not looking to drift or race in it it's my day to day drive and I just want to lower it for aesthetic appeal. Will not having the sway bars affect my cars performance?

I have a 2002 gmc sonoma and I was attempting to replace the oil pressure gauge stepper motor and I forgot to mark the position of the needles. How can I adjust it so it will become accurate?

I have a 1997 Buick lesaber v6 engine. I keep trying to start the engine but it won't catch. There's no clicking or anything.?

It starts to turn over and then won't catch. Normally after I leave it alone it starts fine but I'd like to know what's wrong with it so I can fix it

Why isn't my left turn signal working?

I have a GY6 150cc scooter. i was given a moped by a neighbor who didn't have anyone to sell it to. so i have the moped that has 1 mile and it was never used in 5 years. after my neighbor gave it to me i have replaced all electrical switches. But now here's the problem i flip on the left signal its not working. I flip the right and, it turns on. I have taken apart the cover to the wires and find that 3 wires are missing a connection. One wire is from the speedometer. the other wire is from the headlights and to the battery. Also one wire i find is a double connector. I try to connect them but, when i do they make a spark so i know that's wrong. So i have gone to ebay and ordered the parts and and waited 3 days. after that i have opened the mail and went to the moped and checked the the switch the right turned on, but left isn't turning on. What the buck is going on here?